1. Field of the Invention
This invention relates to hydraulic control valves and more particularly to an improvement in spool control valves whereby the spool is fixed against spinning about its axis.
2. Description of the Prior Art
It is well known that the spool of a hydraulic control valve rotates within the valve body at enormous speeds produced by flow patterns that are directed tangential to the outer spool surfaces. It has been determined that the spool of a 1/4 inch valve can spin at approximately 2200-2500 revolutions per minute due to this phenomena. Generally the spool is supported within the valve on lands formed at spaced intervals on the inner surface of the valve body that provide cylindrical surfaces upon which mating spool surfaces fit. Usually a thin film of hydraulic oil occupies the space between the spool surface and the valve lands, but as spool spin attains high speed the oil film is dispersed, the spool wobbles in addition to spinning, and the mating support surfaces wear. This wear accrues at extraordinary rates: an 1/8 inch valve was found to have had the contacting spool-valve surface worn beyond tolerable limits in six hours.
This problem inherent in spool control valves has typically been accommodated by manufacturers by specifying a reduced flow rate for the valves when operating to deenergize the hydraulic system since spool spin can be reduced or eliminated as flow rates through the valve are minimized. In actual practice the specified flow rate for draining or deenergizing a system is substantially less than the flow rate capacity such valves would have if spool spin could be eliminated.